3D printing at the nanoscale

Abstract

Since the invention in 1980s, 3D printing, also known as additive manufacturing, has been emerging as a disruptive route to manufacturing due to its simple, design friendly manner. In the early stage, 3D printing was intensively used as a primary tool for “rapid prototyping”, fast fabrication of a scale model to inspect the design. Recently, beyond the prototyping, accumulated researches have focused on utilization of 3D printing for manufacturing real 3D products that can function. It has the potential to unify the traditional manufacturing steps such as cutting, milling, welding, and give new ways for customizing products in biomedicine, electronics, buildings, etc. However, the practical realization faces a number of longstanding challenging issues: (1) poor precision (spatial resolution), (2) low throughput, and (3) limited printable material spectrum. Exploiting a nano-sized printing nozzle to deliver ultra-small volume material ink in a meniscus or a droplet form has been emerging as a powerful strategy to improve the spatial resolution in 3D printing. These approaches successfully enable sub-100 nm feature size in nozzle-based 3D printing. This thesis introduces novel strategies to advance nozzle-based 3D nanoprinting in two aspects: new material and improvement of throughput. First, we demonstrate the 3D printing of organic-inorganic metal halide perovskites, the most promising optoelectronic material. The key idea is to localize supersaturation-induced perovskite crystallization into a femtoliter-volume ink meniscus formed on a nanopipette and its omnidirectional guiding enables freeform creation of perovskites 3D nanostructures with an aligned crystalline. Beyond just making a leap into three-dimension, our method provides unprecedented, on-command controls over the dimensions of 3D perovskite nanostructures. Successful demonstrations of 3D printed perovskite nanostructures such as nano-pillars, nano-meshes, and nano-walls are presented. We are conducting research to advance perovskite 3D printing techniques with programmed chemical compositions for RGB 3D nanopixels and heterojunctions. Second, we develop a strategy to realize parallelization scheme in the meniscus-guided 3D nanoprinting. A central requirement is to form multiple menisci by nanopipette arrays with a high reliability. The key idea is to exploit electrohydrodynamic (EHD) dispensing to form multiple menisci in parallel without physical contact or positional feedback. The resulting menisci are successfully used for parallel 3D nanoprinting with high uniformity and reliability by their omnidirectional guiding process. We expect this work to provide a minimalist and cost-effective manner to improve the productivity in nanoscale 3D printing. Third, we develop a strategy to enable parallel EHD 3D nanoprinting in a droplet form. The practical realization has long been restricted by the cross-talk of electric field among the parallelly arranged nozzles, which is regarded as an eliminated factor. In this study, we discover the electric field cross-talk of parallel nozzle apertures can steer the microscopic ejection paths of the ink at will. We exploit this discovery to develop a scalable EHD protocol for on-demand control over shape, placement, and material mixing in 3D printed nanostructures. The main contribution of this thesis is to provide insights into improving material spectrum and throughput in nanoscale 3D printing, the basic step towards becoming a true-manufacturing platform.